Effect of high pressure combined with mild heat or nisin on inoculated bacteria and mesophiles of goat's milk fresh cheese

The effect of pressures ranging from 400 to 500 MPa combined with mild heat on Staphylococcus carnosus inoculated in fresh cheese and the concurrent use of 500 MPa and nisin to inactivate cheese indigenous populations has been studied. Staphylococcus carnosus counts could not be substantially decreased with treatments at 500 MPa at 10 or 25°C for 30 min, whereas treatments at 50°C for 5 min caused a reduction of 7-log10cfu g−1. Multiple-cycle treatments of 500 MPa and times between 15 and 30 min also improved the inactivation rate. Combination of 500 MPa and nisin was the most effective treatment to inactivate cheese indigenous microbiota. Inactivation of Bacillus subtilis spores inoculated in fresh cheese has also been studied. Germination treatments of 60 MPa at 40°C for 210 min followed by vegetative cells inactivation treatments of 500 MPa at 40°C for 15 min caused a lethality of 4·9-log10ofB. subtilis , whereas the same combination of treatments applied at 25°C only caused a 2·7-log10reduction.